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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.

Wednesday, April 20, 2022

SPC Apr 20, 2022 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1247 AM CDT Wed Apr 20 2022 Valid 201200Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL OKLAHOMA INTO SOUTHEAST KANSAS AND EXTREME SOUTHWEST MISSOURI/NORTHWEST ARKANSAS... ...SUMMARY... A few supercells are possible late this afternoon and evening from southeastern Kansas to central/eastern Oklahoma. A few strong storms may also impact areas west of the Oregon Cascades, accompanied by at least some risk for severe weather. ...Eastern OK/Southeast KS Vicinity... An upper-level shortwave trough over the central/southern Rockies at the beginning of the period will shift east across the Plains during the afternoon and early evening. Deep-layer flow is not forecast to be overly strong, with around 30-40 kt expected from around 850-500 mb. However, vertically veering profiles will support effective shear magnitudes around 40-45 kt. At the surface, low pressure over central KS will weaken through the day, with an elongated area of low pressure extending from central/eastern KS into western/central OK by late afternoon. A dryline is forecast to develop eastward across central OK/KS, becoming positioned from southeast KS to just west of the Tulsa vicinity into south-central OK and then southwestward into central TX. Southerly low-level flow will transport low to mid 60s dewpoints northward across eastern OK and southeast KS by peak heating. As midlevel lapse rates steepen with the approach of the upper trough, this will aid in moderate to strong destabilization by late afternoon. This large-scale pattern will generally support a few supercell storms from late afternoon into the evening. However, the forecast remains uncertain/conditional. The timing of the shortwave trough may be sub-optimal for convection. If it ejects east faster than anticipated, subsidence could limit convective initiation across much of the Slight risk area. Furthermore, forecast guidance has become clustered into two camps: 1. convection developing over far northeast OK/southeast KS into southwest MO. 2. convection developing from central to northeast OK and spreading southeast into southeast OK. Most guidance is consistent in maintaining a stronger cap further north where temperatures will remain somewhat cooler, and northward transport of better-quality boundary-layer moisture is even more in question compared to further south. Any convection that does develop from southeast KS into southwest MO likely will be contending with stronger inhibition and a narrower moist warm sector, though will still conditionally support large hail. Most guidance is consistent in the dryline developing eastward to roughly the I-35 corridor with a dryline bulge across northeast OK just west of Tulsa. This area near the I-44 corridor from near/just east of OKC into northeast OK appears the most likely area for a couple of supercells in the 22-02z time frame. Favorably curved low-level hodographs becoming elongated above 3 km will support supercells capable of large hail (some possibly near 2 inches in diameter). Boundary-layer moisture is still expected to be somewhat shallow, and storms may be higher-based initially, though some threat will still exist for a tornado or two given adequate low-level shear and an increasing southwesterly low-level jet during the evening. Elevated convection will spread eastward during the late evening across parts of northern AR and central/southern MO. This activity will mainly pose a threat for marginally severe hail. ...Western OR... Southwesterly deep-layer flow will increase as a Pacific upper trough shifts east toward the Pacific Northwest. Cooling aloft will result in steep lapse rates and modest destabilization is expected west of the Cascades. Deep-layer flow will remain mainly uni-directional, however increasing speed with height will result in moderate effective shear magnitudes around 25-35 kt. This should support a few organized cells. Cold temperatures aloft and elongated hodographs suggest hail will be possible, in addition to locally strong gusts, with stronger convection. A tornado also will be possible, though weak instability and modest SRH may temper this potential. ..Leitman.. 04/20/2022 Read more CHECK UPDATE ZOOM GRAPHIC